Soil in Liwa, Lampung, Sumatra Island, Indonesia

In general, the southern region of Liwa (West Lampung, Sumatra Island) is covered by the residual soil. Soil residues in this region formed by weathering processes are in-situ in the parent rock without experiencing erosion or transportation. Condition tropical regions resulted in the formation of residual soil in Liwa area controlled by the degree of chemical weathering. Climatic and topographic factors also indirectly affect the soil formation process in Liwa area because of these factors helped determine the level of weathering and the thickness of the residual soil. Soil residues from the Liwa area derived from volcanic rock deposition filled up most of volcano hills and valleys. Residual soil weathering is the result of volcanic material such as tuff which has the highest plasticity and high compressibility. It also has a characteristic level of intensive consolidation (Wesley, 1988).

The residual soil in this area can be divided into two types based on their physical appearance. Brown residue on the soil top layer of 0-3 m, whereas below this layer is a red residual soils with a depth> 3 m. They are on the horizon E and B according to the classification of soil profiles according to Soil Survey Staff. Brown residue in the soil on eluviated horizon (E horizon) is characterized by light brown color, many lost their silicate minerals, clay, iron elements, or aluminum due to the washing process and leaving sand or silt particles of minerals resistant. Ground red residues are on illuviated horizon (B horizon) is characterized by red, mineral concentration washing process results in the form of clay minerals, carbon, sesquioxides of iron and aluminum elements.

DETAILS OF GEOTECHNICAL CHARACTERISTIC IN THIS AREA:

·                     Consolidation and compressibility tests showed a tendency to brown residual soil settlement properties (decrease in building construction) are high enough compared with the residual red soil. In accordance with the thickness, consolidation brown residue on the soil is estimated to occur up to 3 m.

·                     Based on the compaction test, natural water content of soil residues (brown and red) are high and are slightly above the optimum water content. As piling material, it is necessary to obtain some degree of drying for the maximum resistance power.

·                     The flow of water occurs vertically from top to bottom through the soil horizons. This process is triggered so that the leaching process of accumulation of minerals often found in the layer B (red residual soil) as enrichment. Lateral water flow at the surface and the erosion is minimal, so that the process of formation of sedimentary soil less than the residual soil widespread in this region.

·                     Soil residues in this region (brown and red) are loaded with halloysite clay minerals, high plasticity value, so that is sensitive to the effects of vibration and changes in pore water pressure. In saturated conditions can cause instability and prone to landslides, especially on steep slopes.

Tectonic and Structure Geology of Sumatra Island

Sumatra Island is located in the path of volcano (NW-SE). Sumatra volcanic arc was formed by the meeting of two plates, the Indo-Australian plate which plunge down into Eurasian plate. The converging between the two plates as more detailed formed tectonic elements as follow:

• Active subduction zone, manifested by the Java-Sumatra Trench.

• Non-magmatic arc as accretionary wedge that formed island of Nias, Simeule Island, Mentawai Islands, etc..

• Fore arc basin, manifested by Sibolga Basin and Bengkulu Basin.

• Magmatic arc, indicated by the Barisan Mountains. Volcanoes located in the Barisan Mountains including Mount Merapi, Mount Kerinci, etc..

• Back arc basin, manifested by the Malacca Straits.

• Continental shelf of Sundaland.

Structure Map of Sumatra Island (Darman & Sidi, 2000)

Important symptoms that occur in Sumatra, in addition to that described above is the presence of horizontal Sumatra fault, known as the Sumatra Fault System (SFS) which divides the island of Sumatra, and following the path of the Barisan Mountains from Aceh to the Sunda Strait. There are two thoughts about SFS:

• Allegedly as a consequence of oblique subduction occurred in Sumatera (Katili, 1985).

• The movement was done by collision between India-Eurasia plate which extruded blocks of Southeast Asia toward Southeast (Tapponier, 1982).

In general, the process of Barisan Mountains uplifting began in Late Miocene, probably reached its peak at the boundary between the Miocene-Pliocene. This uplifting process is not consistently going on until now as estimated by recent geological features followed by the pattern of tectonics in the Early Pleistocene. Tectonic activity along the island formed massive geanticlines that causing the temperature rise related to rapid intrusion of accumulated magma underneath. It is characterized by increasing of both volcanic activity and lateral movement along Sumatra Fault System. All active tectonic activity over the Sumatra region is considered as the main source of recent earthquakes.

Karst Landscapes

Chemical weathering of rocks rich in carbonates would form a unique landscape such as caves, rivers, underground rivers, and springs. Karst derives from the narrow plains means empty due to the dissolving of the work on the surrounding area. Karst developed in areas that have many limestone with little dolomite. Chemical solubility of limestone become more intense when there are cracks, cracks in the rocks so that erosion comes through the gap and continuous surface to the inside.

Limestone towers and conical hills Southeast of Guilin, China

In general there are four necessary conditions for the emergence of karst. First there must be limestone located close to the surface. However, karst is usually found in the dolomite layer was covered by the very lack of solubility when compared with limestone. Second, limestone be packed with lots of thick and thin layered. If the rock is too permeable then the water will continue to flow without reacting first with limestone. Third, the existence of rivers under the ground upon which consist of soluble rocks while also allowing a lot of heavy downward flow forming subsurface water flow is important in the formation of karst. And the last at least the area must have a rainfall conditions is high enough. Some areas with climate Arid or semi-Arid to form karst, karst formation, although some may appear in the previous period when the climate humid/wet.

Gunung Benau (Benau Mount), Type of Sedimentation and Lithology

Consist of interbedded marl and limestone with intercalation of fine grained sandstone conformably overly shoreface sandstone unit. Marl characteristic by grey, limey, frequent calsitic, rich concretions, and pyrite nodules, bioturbated, fossils, minor mica and carbon, concretion. The marl interbedded with light grey, hard, massive, calcite veined, micritic limestone. This well bedded micritic limestone indicate a platform environment. Some build up reef limestone and minor sandstone were also found in this unit.

There also reef limestone with a great amount of fossils including coral, foraminifera, and gastropod. The reef limestone growth in shallow marine environment and interacted with sea level change. Distribution of the reef limestone is not too far and just only found in several spot. It means that the reef can not grow optimally because the sea level change that makes reef can’t catch up or give up to the sea level. The lack of sunshine and nutrient or large influx of terigeneous clastic sediments could also disturbing the growth of reefal limestone.

The limestone is various. In some place, found grey, massive, micritic, very fine-fine grained (calsilutite-calcarenite), no fossil, calsitic, up to 1.5 metres and has a good thin and thick bedding with the marl. The others is fossiliferous limestone, whitish-yellow, texture compact, largely calsite, shells, gastropods, algae, coral. This unit deposited in shelf and shallow water environment. We can interpret the limestone that the massive, micritic limestone is deposited around the outer shelf, near reef, or barrier reef. The major frame building colonies, heads of algae, gastropods, poorly sorted calsirudite, shells, and very rich cavities, hollows is part of reefal (Biohermal Limestone) as a lense or boulder and surrounded by marl and the pelletal packestone, bioclastic wackestone, and limestone is only a local reef development, and growth after shoreface sandstone unit deposited because of drop sea level phase. This local boundstone with limey sand bodies is part of lagoonal or mid-shelf environment.

The middle section contains a tiny section of minor mica, very fine-grained sandstone that interbedded with limestone and marls. This sandstone indicates deltaic/tidal influence in the platform environment. Probably, this environment just occurred in a short time. The whole unit represents platform sedimentation with some localized reef. Sea level change and tectonic process play role during the deposition. The base of this unit is conformably overlies the shoreface unit .The upper contact is an uncomformity with volcanic rock sequence because airfall tuff overlies the marl-limestone unit.

Tanjung Redeb, North East Borneo Geology

Structure and Tectonics

Structures found in the Tj Redeb consist of folds, normal faults, strike slip faults and lineaments. Faults trend NW-SE and SW-NE. Folds trend NW-SE and SW-NE forming anticlines and synclines. This are presumed to have four tectonic events. First event inferred during Late Cretaceous time or older. This event made the Bangara Fm. sediments into folding, faulting and low grade metamorphic rocks. Depositions of Early Eocene shallow marine sediment within the Sembakung Fm. (middle and western part of  area) was also formed Tabalar Fm. in the SE mapped in Eocene-Oligocene and followed by the second tectonic event. Deposition of the Bangara Fm. took place in the middle, east, south and west in the Oligo-Miocene where it is locally intruded by Andesitic rocks, which have been altered and mineralized. Oligo Miocene volcanic activity formed the Jelai Volcanic Rocks in the west. After deposition of the Birang Fm. the Latih Fm was deposited. The Latih Fm. sediments were formed surrounding Teluk Bayur during Late Early Miocene up to Middle Miocene.

The third tectonic event seems to have been occurred after the position of the Latih Fm. Deposition of the Labanan Fm. in the SW and Domaring Fm in the east occurred during the Late Miocene up to the Pliocene whereas the Late Miocene sediments of the Tabul Fm was formed in the north and deposition of the Sinjin Fm. (in SW and N of the sheet). After deposition of the Sinjin Fm. the Sajau Fm. was deposited in the Eastern portion of the sheet in the Plio-Pleistocene.

The Late Pleistocene, after deposition of the Sajau Fm. sediments, the fourth tectonic event was presumed to have occurred. This was showing folding and faulting sediments of the Sajau Fm. and older sediments on the lower part to form the recent topography and morphology.

Mineral and Energy Resources

Coal is one of natural resources having a good prospect in the studied area. The coal surveys were carried out since the Netherlands Indies Government and then continue investigating by the Indonesian Government. Coals are found within sediments of the Latih, Tabul, Labanan and Sajau Formations. The coal mining was formerly carried out by the NV Steenkolen Maatschappij Prapatan (SMP).

Previous geologists report 70 coal seams ranging from 20cm to 5.5 M in thickness. There are many varieties of coal grading from bituminous coal to brown coal. The bituminous and sub-bituminous coals have a quality of 6000 calories per gram. The Teluk Bayur coals have 7000 calories per gram. Building materials such as quartz sand and clays are widespread in Teluk Bayur and Labanan areas. Good quality limestone outcrops are found in Tanjung Selor but are limited in area. The limestone also crops out well in Siduung River upstream but it is hard to be mined because of bad transportation. Limited andesite outcrops were also found in the west and they were used by the logging company for building roads.

Situmorang, R.L. and Burhan, G., 1995

Regional Stratigraphy

• Qa – Quaternary alluvium, Mud, silt, sand, cobbles, pebbles and peat, grey to blackish colors, Unit thicknesses up to 40M..
• Ql – QUATERNARY REEF LIMESTONE, Reefal, coralline and brecciated corals, white to grey, brown, crystalline, hollows, containing corals, locally brecciated, deposited in shallow marine environment.
• TQps – SAJAU Fm. Alternations of claystone, siltstone, sandstone, conglomerate, intercalations of coal seams, contains molluscs, quartzite and micas. Shows cross bedding and lamination. Coal seams 20-100CM thick, black to brown. Unit thickness about 775M deposited in fluviatile and delta environments..
• Tps – SINJIN Fm. Alternations of tuff, agglomerate, lapilli, pyroxene andesite lava, silicified tuff, tuffaceous claystone and kaolin. Contains lignite, quartz, feldspar and black minerals. Unit thickness up to 500M.
• Tmpd – DOMARING Fm. Coralline limestone, chalky limestone, intercalations of marl and lignite; deposited in swampy-littoral environment, thickness is about 1000M. Of Late Miocene-Pliocene Age.
• Tmpl – LABANAN Fm. Alternating polymic conglomerate, sandstone, siltstone, and claystone, intercalations of limestone and coal seams (20-150CM thick) deposited in fluvial environment. Thickness is about 450M. Late Miocene-Pliocene age.
• Tmt – TABUL Fm. Consisting of sandstone, claystone, conglomerate and coal seam intercalations. Contains Operculina sp. Unit thickness about 1050M. Deposited in delta, regressive environment. Late Miocene age.
• Tml – LATIH Fm. Quartz sandstone, claystone, siltstone and coal in the upper part. Intercalations of sandy shale and limestone in the lower part. Black and brown coal seams 0.2 to 5.5M thick. Deposited in estuary, delta and shallow marine environments. Unit thickness is about 800M. Early Miocene to Late Miocene age.
• Tomj – JELAI VOLCANICS, Volcanic breccia, tuffaceous sandstone and tuff. Locally intercalated with coal seams, shows graded bedding and cross bedding structures. Andesite cleave intrusive. Unit thickness reached 200M. Oligocene to Miocene age.
• Tomb – BIRANG Fm. Alternations of marl, limestone and tuff in the upper part. Alternations of marl, chert, conglomerate, quartz sandstone and limestone in the lower part. Thickness is about 1100M. Fossils content: Lepidocyclina ephicides, Spiroclypeus sp., Miogypsina sp., Marginopora vertebralis, Operculina sp., Globigerina tripartite Koch, Globigerinita altispira, Globorotalina mayeri Cushman and Ellisor, Globorotalia peripheronda, Globigerinoides immaturus, Globigerinoides sacculifer, Pre-Orbulina transitoria, Uvigerina sp., and Cassidulina sp. Fossils range Oligocene-Miocene Age.
• Teot – TABALAR Fm. Lower part consist of grey marl, sandstone, shale and intercalations of limestone and basal conglomerate. Upper part consists of dolomite and calcarenite and marl intercalations. Deposited in fluvial-shallow marine environment. Thickness is about 1000M. Eocene to Oligocene age.
• Tes –SEMBAKUNG Fm. Claystone, siltstone and sandstone in the lower part. Quartz sandstone, sandy limestone, chert and tuff in the upper part. Contains fossils: Nummulites sp., Discocyclina sp. Operculina sp. Globigerina sp. Reusella sp. Nodosaria sp., Planulina sp., Amphistegina sp., and Borelis sp., Unit thickness up to 1000M. Deposited in marine environment. Eocene age.
• Kbs – BANGARA Fm. Alternations of metamorphic claystone, silicified claystone, black claystone and shale intercalated with laminated tuffs containing radiolaria. Flysch deposit.
• Tomi – INTRUSIVE ROCKS, Andesite, consisting of vitrophyre, prophyllitic andesite and pyroxene andesite lavas.

Geology of Lomblen Island, Indonesia

Regional Geology and Stratigraphy

Regional structure Lomblen Island include of Banda arc Volcanic belt, with structure terms as folding and faulting in NE-SW and SE-NW direction. The oldest rock formation is Kiro Formation (Tmk) in lower Miocene until upper Miocene. This formation consist of lava, breccias, agglomerate implied layered tuff. Kiro formation wedge with Nangapanda formation (Tmn) that consisted of sandy tuff, breccias tuff, and implied by limestone. Those old formation above were infiltrated by granodiorite (Tmd) in upper Miocene. When Pliocen-Plistocene there was volcanic activity such as lava, agglomerate, and tuff.


 

Regional Stratigraphy of Lomblen Island (Noya, Y., and Suwarno, N., 1983)
 

Structure Characteristics

By regional investigation in field, map of topography and interpretation photograph air there are 2 especial structure direction that is: north-south direction and northeast-southwest direction. In this area (Atedai) there are 6 big structure they are lineament, volcano, cauldron, crater, caldera, slide and fault.

Lineament

This lineament structure have the direction NW-SE. This structure is the oldest big structure estimated cut the basement. Alongside this lineament have emerged the volcano network, such as: Watulolo, Atolojo, Watukuba etc.

Cauldron (crater of Atolojo)

This cauldron structure is the result of eruption mount Atolojo, which among other things yield fallout sediment of pyroclastic skoria andesitic. Cauldron diameter 750-1000 m encircling from NE till NW and open toward north.

Caldera Watukuba

This structure is the result of eruption Watukuba yielding dusty sediment of pyroclastic. diameter of caldera Watukuba 2500 m encircle from north direction to west till easterly. In floor of caldera there are geothermal manifestation like hot ground and alteration.

Debris Avalanches/sliding of Wai Teba

This structure represent the slide which have association with the weak area, form like horse poultice that opening eastwards of Watuwawer.

Fault of Wai Kowan

Fault structure have the direction NE-SW. Alongside this structure have attended the hot water source of Wai Kowan, hot ground of Koti and area of alteration Lowo Kebingin.

Fault of Lewoderoma

This structure have the direction NE-SW. As long as this structure have emerged the hot water source of Lewoderoma And hot water of Waiketi.

Geomorfology

Regional area of research by Volcanology Department of Indonesia divided in 5 morphology region:

1. Old volcanic
2. Mount Watuloko
3. Mount Watukuba and Atalojo
4. Debris Avalanches unit
5. Plain morphology unit

· Old volcanic
Set of this distinguished by circular hilly. The relief is smooth until middle. Dale instruct north-south direction. River have parallel semi pattern and sentence sharply form in high stadium erosion. Set of this reside in north formed of old rock volcanic.

· Mount Watuloko
Set of this distinguished by topography form which harsh, precipitous level of inclination and erosion river deeply. Set of this take possession of the middle until north of investigation area limited of old morphology volcanic. Set of this built by lava andesitic which is generally escaped because fault.

· Mount Watukuba and Atalojo
Set of this show the very typical topography form that is volcano crater and caldera. There are a crater with the diameter 750-1000 m ( Mount Atalojo) and a caldera with the diameter 2500 m ( Mount Watukuba). Set of this morphology is formed by fallout of sediment of pyroclastic and lava. The river have pattern radial with the narrow tight dale pattern making dominant vertical erosion.

· Debris Avalanches unit
Set of this have the wavy topography form with middle of level inclination. Generally weak river stream and a little erosion. Set of this formed by rock from landslide.

· Plain morphology unit
Set of this located in coast environment formed by rock alluvial. Set of this distinguished by smooth topography.